Numerous methods and catalysts have been described for alkylating aromatic amines to provide valuable and useful chemical products. Among the vast literature on the general subject are some investigations on the use of certain metal oxides as the catalyst and alcohols as the alkylating agent.
Mailhe et al, Compt. rend., 166, 467 (1918), report that while thoria and zirconia are effective as catalysts for the N-methylation of aniline with methanol, alumina is a superior catalyst for this reaction. Six years later Brown et al reported in J. Am. Chem. Soc., 46, 1836 (1924) that silica gel was also effective as a catalyst for the N-alkylation of aniline with methanol, ethanol, propanol and butanol at 300.degree.-500.degree. C.
A group of catalysts for the alkylation of aniline with methanol or ethanol was studied by Shuikin and coworkers, J. Gen. Chem. (U.S.S.R.) 4, 1451-7 (1934) and ibid., 6, 774-9 (1936). The catalysts studied were Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3, Al.sub.2 O.sub.3 --Fe.sub.2 O.sub.3, Al.sub.2 O.sub.3 --SnO, Al.sub.2 O.sub.3 --Cr.sub.2 O.sub.3, Al.sub.2 O.sub.3 --NiO and Al.sub.2 O.sub.3 --ZnO.
Heinemann U.S. Pat. No. 2,515,872 describes a method for producing secondary and tertiary amines, which comprises contacting an aliphatic alcohol of from 1 to 20 carbon atoms and an aromatic amine containing at least one hydrogen atom bonded to the amino nitrogen atom, at a temperature between 450.degree. F. and 600.degree. F. with bauxite thermally activated at 1000.degree. F. to 1200.degree. F. and containing from 4% to 22% of naturally occurring iron oxide.
A further study of the alkylation of aniline with methanol is reported by Hill et al in Ind. & Eng. Chem., 43, 1579-83 (1951). They found that as possible catalysts for the reaction tungstic oxide was not very effective, zinc oxide, chromium oxide and magnesium oxide exerted little influence on the reaction, thorium oxide had little or no activity and that titanium oxide was moderately active. They also found that most of these oxides, including titania, tended to decompose the alcohol reactant.
U.S. Pat. No. 2,580,284 to Deahl et al., describes the production of secondary aromatic amines from primary aromatic amines and alcohols using catalysts that comprise as essential components, metallic copper, alumina and at least one other difficultly reducible oxide. In order of decreasing preference these other oxides are indicated to be calcium oxide, zinc oxide, chromium oxide, magnesium oxide, ferrous oxide, cadmium oxide, and potassium oxide. The patentees also refer to runs involving a feed mixture of aniline, methanol and hydrogen (1:1:2 moles), and the following catalysts (the proportions of which are unspecified): copper, manganese oxide, alumina, and "catalysts containing the oxides of . . . strontium, molybdenum or vanadium." Substitution of nickel or silver for metallic copper in the Deahl et al. catalysts is shown to result in very poor conversions, as did the replacement of the alumina with a diatomaceous earth.
Inoue et al, Sekiyu Gakkai Shi 15, No. 5, 372-8 (1972), describe the methylation of aniline and o-toluidine with methanol and an aluminum oxide-magnesium oxide catalyst.
The use of copper chromite as a catalyst in the alkylation or phenylation of anilines with alcohol or phenol was investigated by Nakagawa et al--see Japan Kokai Tokkyo Koho 73-49,727 (laid open in July 1973) and 77-48,969 (laid open in December 1977).
Murai et al. U.S. Pat. No. 3,819,709 refers to the synthesis of N-methylaniline in a liquid phase reaction between aniline and methanol using a catalyst consisting of (a) copper or (b) a chromium catalyst, e.g., Cr.Cu.O, Cr.Zn.O, Cr.Ni.O, Cr.Fe.O, Cr.Mo.O, Cr.Cu.BaO, Cr.Cu.Mn.O, etc., in which the chromium content is 20-80 weight percent, the Cu, Zn, Mi, Fe or Mo content is 20-80 weight percent, and the content of Ba, Ca, Mg or Mn is 0-5 weight percent.
Catalytic ring alkylation of phenylamines with alcohols using an alumina and molybdenum oxide catalyst is described in U. S. Pat. No. 3,868,420 (granted in February 1975 to Evans et al).
Takamiya et al in Waseda Daigaku Rikogaku Kenkyusho Hokoku 69, 21-25 (1975) report the results of the study of the vapor phase catalytic N-methylation of aniline with methanol with certain transition metal zeolites as catalysts. They found that the catalytic activity of the metal ion was Zn.sup.2+ &gt;Co.sup.2+ &gt;Ni.sup.2+ &gt;Mn.sup.2+ &gt;Cu.sup.2+.
Matsumoto et al., Japan Kokai Tokkyo Koho 76-75029 (laid open in June 1976) describes nuclear methylation of xylidine with methanol using as catalyst alumina-silver oxide, silica alumina-silver oxide, alumina-chromium oxide, alumina-vanadium oxide, titanium oxide-zinc oxide or titanium oxide-zirconium oxide.
Japan Kokai Tokkyo Koho 78-90227 (laid open in August 1978) to Motoyama et al teaches the use of silica-alumina as the catalyst for reaction between primary aromatic amines with alcohols or ethers.
In U.S.S.R. Patent No. 644,526 (issued in January 1979 to Dobrovol'skii et al) catalysts containing copper oxide, barium oxide, chromium oxide and titanium oxide for alkylation of aromatic amines with alcohols are described.
U.S.S.R. Patent No. 666,167 (issued in June 1979 to Esipov et al) refers to the use of nickel oxide as a catalyst for the alkylation of aniline with alcohols.
Takamiya et al, Nippon Kagaku Kaishi, 1979, No. 11, 1453-7, describe the N-methylation of aniline with methanol over a magnesium oxide catalyst.
U.S. Pat. No. 4,183,868 (granted in January 1980 to Radimerski et al) teaches the alkylation of 2,6-dialkyl anilines with alkanols using a copper oxide-chromium oxide or copper oxide-zinc oxide catalyst containing palladium or platinum. The catalyst, which may also contain small amounts of alkaline earth oxides or alkali metal oxides such as barium oxide or sodium oxide, is activated before use by heating to 120.degree.-350.degree. C. with hydrogen.
U S. Pat. No. 4,351,958 (granted in September 1982 to Takahata et al) describes the alkylation of aromatic amines by reaction with a primary or secondary alcohol using a catalyst containing iron oxide as the main constituent. Although the iron oxide catalysts described in the patent are generally effective, they cause extensive decomposition of the alcohol at useful reaction temperatures. Thus in practice it is not possible to recover unreacted alcohol for recycle or other use.